\(\left\{ \begin{array}{l}\left[ {\overrightarrow u ,\overrightarrow {u'} } \right] e \overrightarrow 0 \\\left[ {\overrightarrow u ,\overrightarrow {u'} } \right]\overrightarrow {MM'}  = 0\end{array} \right.\)    

\(\left[ {\overrightarrow u ,\overrightarrow {u'} } \right] e \overrightarrow 0 \)         

\(\left[ {\overrightarrow u ,\overrightarrow {u'} } \right]\overrightarrow {MM'}  = 0\)            

\(\left[ {\overrightarrow u ,\overrightarrow {u'} } \right] = \overrightarrow 0 \)